Tsuchikane Yuki, Kobayashi Hiroka, Kato Machi, Watanabe Juri, Wu Jiunn-Tzong, Sekimoto Hiroyuki
Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo, 112 8681, Japan.
Division of Material and Biological Sciences, Graduate School of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo, 112 8681, Japan.
J Plant Res. 2018 Sep;131(5):735-746. doi: 10.1007/s10265-018-1043-8. Epub 2018 Jun 8.
Reproductive isolation is essential for the process of speciation. In order to understand speciation, it is necessary to compare one mating group with other phylogenetically related but reproductively isolated groups. The Closterium peracerosum-strigosum-littorale (C. psl.) complex is a unicellular isogamous zygnematophycean alga, which is believed to share a close phylogenetic relationship with the land plants. In this study, we identified a new mating group, named group G, of C. psl. complex and compared its physiological and biochemical characteristics with the mating group I-E, which was closely related to the mating group G. Zygospores are typically formed as a result of conjugation between mating-type plus (mt) and mating-type minus (mt) cells in the same mating group during sexual reproduction. Crossing experiments revealed mating groups G and I-E were reproductively isolated from each other, but the release of lone protoplasts from mt cells of mating group G was induced in the presence of mt cells of mating group I-E. In fact, the sex pheromone, protoplast-release-inducing protein of mating group I-E induced the release of protoplasts from mt cells of mating group G. When mt and mt cells of both mating groups I-E and G were co-cultured (multiple-choice matings), the zygospore formation of mating group G, but not that of mating group I-E, was inhibited. Based on these results, we propose a possible mechanism of reproductive isolation between the two mating groups and suggest the presence of sexual interference between mating group G and mating group I-E.
生殖隔离是物种形成过程中的关键环节。为了理解物种形成，有必要将一个交配群体与其他系统发育相关但生殖隔离的群体进行比较。三角褐指藻-条纹褐指藻-滨海褐指藻（C. psl.）复合体是一种单细胞同配接合的双星藻目藻类，被认为与陆地植物有着密切的系统发育关系。在本研究中，我们鉴定出了C. psl.复合体的一个新交配群体，命名为G组，并将其生理生化特征与与G组密切相关的I-E交配群体进行了比较。在有性生殖过程中，合子通常是同一交配群体中交配型正（mt）和交配型负（mt）细胞之间结合的结果。杂交实验表明，G组和I-E组彼此生殖隔离，但在I-E组mt细胞存在的情况下，能诱导G组mt细胞释放单个原生质体。事实上，I-E组的性信息素、原生质体释放诱导蛋白能诱导G组mt细胞释放原生质体。当I-E组和G组的mt和mt细胞共培养（多重选择交配）时，G组的合子形成受到抑制，而I-E组则不受影响。基于这些结果，我们提出了两个交配群体之间生殖隔离的可能机制，并表明G组和I-E组之间存在性干扰。
